Unraveling the reactivity of a cationic iminoborane: avenues to unusual boron cations

A cationic terminal iminoborane [Mes*N[triple bond, length as m-dash]B ← IPr(2)Me(2)][AlBr(4)] (3(+)[AlBr(4)](−)) (Mes* = 2,4,6-tri-tert-butylphenyl and IPr(2)Me(2) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) has been synthesized and characterized. The employment of an aryl group and N-heterocyclic carbene (NHC) ligand enables 3(+)[AlBr(4)](−) to exhibit both B-centered Lewis acidity and BN multiple bond reactivities, thus allowing for the construction of tri-coordinate boron cations 5(+)–12(+). More importantly, initial reactions involving coordination, addition, and [2 + 3] cycloadditions have been observed for the cationic iminoborane, demonstrating the potential to build numerous organoboron species via several synthetic routes.